The invention relates in general to microelectromechanical (MEMS) devices and in particular to MEMS devices that provide deflection out of the plane of the MEMS substrate.
Conventional systems for guiding missiles or projectiles in flight use canards, or small wing-like structures, to steer the projectile. These structures are large (approximately 3″ in length) and require motors to actuate. The stabilizing fins on the projectile have to be increased in size to counteract the effect the canards have of moving the center of pressure forward.
A MEMS control surface can reduce drag and hence increase the range of projectiles by eliminating the drag associated with canards and reducing the drag of the fins. In addition, MEMS control surfaces may reduce volume, weight, and power requirements, further increasing the projectile's range. Another added benefit of the MEMS control surface is the reduction of cost associated with batch fabrication techniques.
Known MEMS devices for producing a mechanical deflection include various types of thermally actuated beams, including cantilever and arch beams. These beams have proven successful in producing a deflection in the plane of the MEMS substrate. Devices such as projectile control surfaces, however, require a deflection out of the plane of the MEMS substrate, that is, in a direction perpendicular to the MEMS substrate.
One MEMS type apparatus that provides out-of-plane deflection is shown in U.S. Pat. No. 5,824,910 issued on Oct. 20, 1998 and entitled “Miniature Hydrostat Fabricated Using Multiple Microelectromechanical Processes.” Another MEMS type apparatus that provides out-of-plane deflection is shown in U.S. Pat. No. 6,069,392 issued on May 30, 2000 and entitled “Microbellows Actuator.” These two U.S. patents are expressly incorporated by reference. A third MEMS type apparatus that provides out-of-plane deflection is shown in U.S. Pat. No. 6,474,593 issued on Nov. 5, 2002 and entitled “Guided Bullet.”
The vertical deflection of a single diaphragm actuator, like the hydrostat mentioned above, is limited by the diameter of the diaphragm and its thickness. A micro bellows actuator is able to deliver much greater vertical deflections for a similar sized device. However, the deflections required to make an effective control surface are many times greater than a micro bellows alone can provide. The electrostatically actuated curved beam shown in U.S. Pat. No. 6,474,593 cannot withstand high-speed flow forces. A suitable control surface can be realized by combining a micro bellows actuator with a ramp capable of being rotated out of plane.